Changes In Frequency Response Research Articles

Focus on sensors and detectors

Focus on sensors and detectors

Fundamental Properties of Linear Ship Steering Dynamic Models

This paper is concerned with the fundamental properties associated with the Nomoto models. Specifically ,the state space model associated with the first order Nomoto model is both observable and controllable. The state space model associated with the second order Nomoto model is also observable ; however, it is controllable only if the effective sway time constant is different from the effective yaw time constant. The zero appearing in the transfer function model is found responsible for the overshoot behaviors ,which are typical in the yaw rate for large rudder angle steering. This suggests that a second order Nomoto model is more appropriate if the overshoot feature is to be properly modeled. Both the first and second order Nomoto transfer function models are identifiable ,with an ill-conditioning problem associated the latter. This makes the first order Nomoto model very popular in the adaptive autopilot applications. Model reduction for a fourth order transfer function ship modeled scribing the sway-yaw-roll dynamics is conducted to reach the second order Nomoto model describing the sway-yaw dynamics and the first order Nomoto model describing the yaw dynamics it self, and the Bode plots for these models are given to show the changes in system frequency response caused by model simplification. Thus, appropriate model structures can be selected according to the intended frequency range of application to meet the modeling accuracy requirements.

NO in the caudal NTS modulates the increase in respiratory frequency in response to chemoreflex activation in awake rats

The role of nitric oxide (NO) in the caudal NTS (cNTS) on baseline cardiovascular and respiratory parameters and on changes in respiratory frequency (fR) and cardiovascular responses to chemoreflex activation was evaluated in awake rats. Bilateral microinjections of l-NAME (200nmoles/50nL), a non-selective NO synthase (NOS) inhibitor, into the cNTS increased baseline arterial pressure, while microinjections of N-PLA (3pmoles/50nL), a selective neuronal NOS (nNOS) inhibitor, did not. l-NAME or N-PLA microinjected into the cNTS reduced the increase in fR in response to chemoreflex activation but not cardiovascular responses. These data show that (a) NO produced by non-nNOS in the cNTS is involved in the baseline autonomic control and (b) NO produced by nNOS in the cNTS is involved in modulation of the increase in fR in response to chemoreflex activation but not in the cardiovascular responses. We conclude that NO produced by the neuronal and endothelial NOS play a different role in the cNTS neurons integral to autonomic and respiratory pathways.

Changes in gape frequency, siphon activity and thermal response in the freshwater bivalves Anodonta cygnea and Margaritifera falcata

Physiologically-driven rhythms in bivalve molluscs are predicted to vary as a function of metabolic rate and temperature, in contrast to genetically predisposed biological clocks. These rhythms can be evaluated using long-term video monitoring techniques under controlled conditions in laboratory aquaria. The bivalves Anodonta cygnea and Margaritifera falcata were used to evaluate the effect of temperature on rhythms in gape and the formation of siphons at the mantle edge. Frequency and duration of shell closure vary with temperature in both species, but with different responses. Mean duration of intervals of valve closure decreases as temperature rises in both species, and is consistent with physiological limitation by increased biological oxygen demand. For A. cygnea, cumulative gape duration peaks at 25°C, with less time spent closed than at any other temperature, but increasing temperatures correspond to an increase in gape frequency with a strong increase observed at 31°C. In contrast, frequency of adduction and valve closure peak at 25°C in M. falcata, and continuous gaping is observed above 29.5°C. This physiological stress is consistent with evidence from sclerochronologically-calibrated stable isotope studies of shells, where growth breaks in many marine taxa coincide with maximum temperatures above 31°C as derived for δ18Ocarbonate. The results of this study suggest that these growth breaks may be due to physiological limitations in oxygen uptake and metabolic activity, rather than being a direct consequence of elevated temperature alone.

Acute changes in frequency responses of inferior colliculus central nucleus (ICC) neurons following progressively enlarged restricted spiral ganglion lesions

Immediate effects of sequential and progressively enlarged spiral ganglion (SG) lesions were recorded from cochleas and inferior colliculi. Small SG-lesions produced modest elevations in cochlear tone-evoked compound action potential (CAP) thresholds across narrow frequency ranges; progressively enlarged lesions produced progressively higher CAP-threshold elevations across progressively wider frequency ranges. No comparable changes in distortion product otoacoustic emissions (DPOAEs) amplitudes were observed consistent with silencing of auditory nerve sectors without affecting organ of Corti function. Frequency response areas (FRAs) of inferior colliculus (IC) neurons were recorded before and immediately after SG-lesions using multi-site silicon arrays fixed in place with recording sites arrayed along IC frequency gradient. Individual post-lesion FRAs exhibited progressively elevated response thresholds and diminished response amplitudes at lesion frequencies, whereas responses at non-lesion frequencies were either unchanged or enhanced. Characteristic frequencies were shifted and silent areas were introduced within these FRAs. Sequentially larger lesions produced sequentially larger shifts in CF and/or enlarged silent areas within affected FRAs, producing immediate changes in IC frequency organization. These results contrast with those from the auditory nerve, extend previous reports of experience-induced plasticity in the auditory CNS, and support results indicating afferent convergence onto ICC neurons across broad frequency bands.

A blind carrier frequency offset estimation scheme for OFDM systems with constant modulus signaling

This paper presents a new blind carrier frequency offset (CFO) estimation scheme for orthogonal frequency division multiplexing (OFDM) systems with constant modulus (CM) signaling. Both single-input single-output (SISO) systems and multiple-input multiple-output (MIMO) systems with orthogonal space-time block coding are considered. The proposed scheme is based on the reasonable assumption that the channel frequency response changes slowly in the frequency domain, which implies that the channel frequency response on two consecutive sub- carriers is approximately the same. Based on this assumption, cost functions are derived in closed-form, which minimize the difference between the signal power of two neighboring subcarriers. The identifiability of the proposed scheme is mathematically proved, which implies that minimizing the derived cost function gives an approximate estimate of the CFO. We demonstrate that the proposed scheme provides an excellent trade-off between complexity and performance as compared to prominent existing estimation schemes.

Damage detection in repairs using frequency response techniques

Structural health monitoring (SHM) technology may be applied to composite bonded repairs to enable the continuous through-life assessment of the repair’s efficacy. Adhesively bonded joints are an ideal starting point for real-time, in situ monitoring due to known mechanisms and locations of failure. Similarly, the ability to accurately monitor the health of a joint has potential to aid acceptance of adhesive bonding. This paper describes the development of an SHM technique for the detection of debonding in composite bonded patches based on frequency response. Two commonly used repair schemes, the external doubler repair and the scarf repair, are examined. The paper outlines an experimental investigation on the frequency response of the repairs with and without defects under different boundary conditions. It was found that damage could be readily detected through changes in frequency response for both types of repair. The results are discussed with implications for the development of a technology to monitor the integrity of composite bonded repairs.

Phononic band gap crystals with periodic fractal inclusions: Theoretical study using numerical analysis

A numerical study is conducted using finite difference time-domain analysis to determine the impact of periodic fractal-shaped inclusions on the frequency response of two-dimensional phononic or acoustic band gap crystals. Both solid host with solid inclusions and solid host with fluid inclusions were studied with increasing fractal order iteration or increasing fractal dimensionality for different types of fractals generated from square inclusions in a square lattice formation. Solid-fluid systems showed marked changes in frequency response including increasing multiplicity of bands compared to regular square inclusion shapes. Fractal inclusions in the solid host/fluid inclusion systems studied exhibited the ability to provide band gaps for much longer wavelengths than those of the solid host/solid inclusion systems studied. This behavior was attributed to the possibility of resonant localization effects that a fractal fluid inclusion can exhibit compared to fractal solid inclusions.

Phage immobilized magnetoelastic sensor for the detection of Salmonella typhimurium

In this article, a phage-based magnetoelastic sensor for the detection of Salmonella typhimurium is reported. Filamentous bacteriophage specific to S. typhimurium was used as a biorecognition element in order to ensure specific and selective binding of bacteria onto the sensor surface. Phage was immobilized onto the surface of the sensors by physical adsorption. The phage immobilized magnetoelastic sensors were exposed to S. typhimurium cultures with different concentrations ranging from 5 × 10 1 to 5 × 10 8 cfu/ml, and the corresponding changes in resonance frequency response of the sensor were studied. It was experimentally established that the sensitivity of the magnetoelastic sensors was higher for sensors with smaller physical dimensions. An increase in sensitivity from 159 Hz/decade for a 2 mm sensor to 770 Hz/decade for a 1 mm sensor was observed. Scanning electron microscopy (SEM) analysis of previously assayed biosensors provided visual verification of frequency changes that were caused by S. typhimurium binding to phage immobilized on the sensor surface. The detection limit on the order of 10 3 cfu/ml was obtained for a sensor with dimensions 1 × 0.2 × 0.015 mm.

Age-weighted sound levels

In many areas where established noise goals, in terms of A-weighted sound levels, have been achieved-particularly in the vicinity of airports, the public remains dissatisfied. A-weighting accounts for the non-uniform frequency sensitivity of human hearing but is based upon data collected from 18-25-yr olds. However, the mean age for the overall U.S. adult population is now almost 50 yr. For this reason, the importance of ageing on the suitability of A-weighted sound levels for assessing annoyance response was examined. Age-corrections were applied to the A-weighting curve and the resultant overall Age-weighted sound levels compared to the corresponding A-weighted sound levels for a variety of spectra. The analyses found that the change in hearing frequency response due to hearing loss typical of aging does not greatly alter the overall frequency-weighted sound levels of common environmental noises. Thus, the A-weighted sound level remains suitable for quantifying the noise exposures for the general population. However, the perception of certain natural sounds is likely to be attenuated with ageing, and its absence may serve to heighten the adverse response to manmade sounds. Overall reductions in hearing sensitivity do appear to be important and may alter the adverse response to noise for many individuals older than 50 yr. Ageing may yet explain some variation in observed annoyance response of individuals, but in terms of age-dependent shifts in overall hearing sensitivity rather than changing frequency response.

Low-gravity liquid nonlinear sloshing analysis in a tank under pitching excitation

Under pitch excitation, the sloshing of liquid in circular cylindrical tank includes planar motion, rotary motion and rotary motion inside planar motion. The boundaries between stable motion and unstable motion depend on the radius of the tank, the liquid height, the gravitational intension, the surface tensor and the sloshing damping. In this article, the differential equations of nonlinear sloshing are built first. And by variational principle, the Lagrange function of liquid pressure is constructed in volume integration form. Then the velocity potential function is expanded in series by wave height function at the free surface. The nonlinear equations with kinematics and dynamics free surface boundary conditions through variation are derived. At last, these equations are solved by multiple-scales method. The influence of Bond number on the global stable response of nonlinear liquid sloshing in circular cylinder tank is analyzed in detail. The result indicates that the system's amplitude–frequency response changes from a ‘soft-spring’ to a ‘hard-spring’ in the planar motion with the decreasing of the Bond number, while it changes from a ‘hard-spring’ to a ‘soft-spring’ in the rotary motion. At the same time, jump, lag and other nonlinear phenomena of liquid sloshing are discovered.

Waveguide model of the hearing aid earmold system

BackgroundThe earmold system of the Behind-The-Ear hearing aid is an acoustic system that modifies the spectrum of the propagated sound waves. Improper selection of the earmold system may result in deterioration of sound quality and speech intelligibility. Computer modeling methods may be useful in the process of hearing aid fitting, allowing physician to examine various earmold system configurations and choose the optimum one for the hearing aid user.MethodsIn this paper, a computer model adequate for this task is proposed. This model is based on the waveguide modeling method. The waveguide model simulates the propagation of sound waves in the system of cylindrical tubes. Frequency response of the hearing aid receiver is simulated in the model and the influence of the ear canal and the eardrum on the earmold system is taken into account. The model parameters are easily calculated from parameters of a physical hearing aid system. Transfer function of the model is calculated and frequency response plots are obtained using the Matlab system.ResultsThe frequency response plots of the earmold model were compared to the measurement plots of the corresponding physical earmold systems. The same changes in frequency responses caused by modification of length or diameter of a selected waveguide section, are observed in both measurement data of a real earmold system and in computed model responses.ConclusionComparison of model responses obtained for various sets of parameters with measurement data proved that the proposed model accurately simulates the real earmold system and the developed model may be used to construct a computer system assisting the physician who performs earmold system fitting.

Physiological and histochemical adaptation of the electrically stimulated gracilis muscle to neoanal sphincter function.

The physiological and histochemical characteristics of the gracilis muscle were studied in 19 patients undergoing electrically stimulated gracilis neosphincter construction. Indications for surgery were faecal incontinence (n = 11) and reconstruction following sphincter excision or congenital absence (n = 8). Transposition of the gracilis muscle around the anal canal followed by chronic low-frequency electrical stimulation was associated with a shift in the frequency-response curve and a prolongation of the time-course of individual muscle twitches suggestive of transformation to a slow-twitch fatigue-resistant type. Temporary cessation of electrical stimulation resulted in a reversal of the frequency-response changes. Muscle biopsies taken before and a median of 80 (range 49-137) days after transposition and low-frequency electrical stimulation indicated a significant increase in the proportion of type 1 fibres and a significant decrease in their diameter. These results show that the human gracilis muscle is capable of physiological and histochemical adaptation to long-term neosphincter function.

A low-cost, high-performance, digital signal processor-based lock-in amplifier capable of measuring multiple frequency sweeps simultaneously

A high-performance digital lock-in amplifier implemented in a low-cost digital signal processor (DSP) board is described. This lock in is capable of measuring simultaneously multiple frequencies that change in time as frequency sweeps (chirps). The used 32-bit DSP has enough computing power to generate N=3 simultaneous reference signals and accurately measure the N=3 responses, operating as three lock ins connected in parallel to a linear system. The lock in stores the measured values in memory until they are downloaded to the a personal computer (PC). The lock in works in stand-alone mode and can be programmed and configured through the PC serial port. Downsampling and multiple filter stages were used in order to obtain a sharp roll off and a long time constant in the filters. This makes measurements possible in presence of high-noise levels. Before each measurement, the lock in performs an autocalibration that measures the frequency response of analog output and input circuitry in order to compensate for the departure from ideal operation. Improvements from previous lock-in implementations allow measuring the frequency response of a system in a short time. Furthermore, the proposed implementation can measure how the frequency response changes with time, a characteristic that is very important in our biotechnological application. The number of simultaneous components that the lock in can generate and measure can be extended, without reprogramming, by only using other DSPs of the same family that are code compatible and work at higher clock frequencies.

Effect of resonator dimensions on nonlinear standing waves

An investigation of the effect of resonator dimensions on nonlinear standing waves in shaped resonators is conducted. Simple forms of the shear viscosity term in the momentum equations are developed for an axisymmetric (2D) resonator and a low aspect ratio rectangular (3D) resonator. The cross sections of the resonators are exponentially expanded and the one-dimensional wave equations are solved by using the Galerkin's method. The quality factors, pressure waveforms, compression ratios, and resonance frequencies are calculated for different dimensionless cross sections and lengths of the resonators. The results show that, apart from the resonator length, the ratio of the cross-section dimension to the length of the resonator is an important parameter. If the ratio is greater than 0.04, the characteristics of the shaped resonator are not affected significantly. However, when the ratio is less than 0.01, the resonance becomes weak, the compression ratio drops substantially, and the frequency response changes as well.

Development of the Two-Step Delamination Identification Method by Resonant and Anti-Resonant Frequency Changes

Identification of the location and size of delamination is important for structural health monitoring of composite laminated structures, since delamination degrades compression stiffness of the structures. In the present study, a two-step delamination identification method using resonant and anti-resonant frequency changes is proposed. It is well known that resonant frequencies are changed depending on the location and size of delamination. As for anti-resonant frequencies, they also change mainly depending on the location of delamination. Since the resonant and anti-resonant frequencies are specified easily in the frequency response function, the present method is low cost and applicable to any structures. The present method is applied to delamination identification of carbon/epoxy cantilever beams, and effectiveness of the present method is discussed. Introduction Recently, composite laminated structures have been applied to many structures of vehicles because of its high specific stiffness and strength. Since interlaminar strength of composite laminated structure is relatively low, internal damage, such as delamination, can be easily induced in service. Since delamination degrades compression strength of the structure, it is necessary to identify the size and location of delamination nondestructively for the assessment of structural integrity. However, conventional nondestructive inspection methods, such as X-ray or ultrasonic inspection, are high cost, and application to large structures is difficult owing to size restriction of the apparatuses. The present study proposes a two-step delamination identification method using resonant and anti-resonant frequency changes. In order to examine effectiveness of the present method, delamination identification of a carbon/epoxy cantilever beam is conducted. As a preparation for delamination identification, the beam is divided into two domains based on the mode shapes. The delaminated domain in which delamination is supposed to exist is first identified from the anti-resonant frequency changes, and the delamination location and size are identified from the resonant frequency changes to the next. In order to analyze frequency response changes caused by delamination, finite element method was applied. Effectiveness of the present identification method was investigated both in analysis and experiment. Symmetry of Resonant Frequency Changes Fig.1 shows schematic of a carbon/epoxy cantilever beam with delamination. The beam is 1.45mm thick, 19mm wide and 200 mm long. The laminate configuration of the beam is [02/902]S, and a through width delamination is existed at one 0/90 interlayer. In order to examine effect of delamination location and size on the resonant frequencies of the beam, modal analyses of the beam were conducted by using ANSYS, a commercially available general-purpose finite element code. Table 1 shows material properties of uni-directional carbon/epoxy lamina used for calculation, where Key Engineering Materials Vols. 270-273 (2004) pp. 1852-1858 online at http://www.scientific.net © 2004 Trans Tech Publications, Switzerland Title of Publication (to be inserted by the publisher) subscript 1 means the direction parallel to the fiber and subscripts 2 and 3 means the direction perpendicular to the fiber. In the present paper, normalized values l/L and a/L are employed to express the delamination location and size respectively, where L is beam length. Fig.2 shows resonant frequency changes of the beam as a function of delamination location obtained by FEM analysis, where delamination size is constant value 0.1. In fig.2, abscissa means delamination location and ordinate means frequency value normalized by the intact value of each mode. In general, reduction of resonant frequency is caused by stiffness reduction of structures. For a composite laminated beam with delamination, reduction of the bending stiffness is caused when shear force acts on the delamination, and shear force distribution of each mode depend on each modal shape. For this reason, the resonant frequency changes of the cantilever beam shows quasi-symmetry in the region defined by 0.3≤l/L≤0.7 except for the first mode, though the cantilever beam is not a symmetric structure. This causes failure in identification of delamination location based on resonant frequency changes [1]. In order to make it possible to identify delamination location in the cantilever beam, another parameters that have information about delamination location and no symmetry. In the present study, anti-resonant frequency is adopted. (L=200mm, b=19mm, h=1.45mm) L h Delamination

Experimental investigation of local damage detection on a 1/15 scale model of a suspension bridge deck

This paper addresses signal processing and applicability of local damage detection algorithms on a 1/15 scale model of the Yeongjong Bridge floor system. As many as 48 channels of dynamic strain data were collected, corresponding to strain gauge placements on the in-situ structure. Model excitation was induced via a series of impact hammer strikes. Twelve different damage cases are examined including connection loosening, chord removal, saw-cuts on the deck plate, and bearing removal simulating hanger failure. Signal anomaly index (SAI) representing the amount of change in frequency response is adopted to detect the presence and type of damage along with a series of neural network classifiers. It is found that SAI and ANN are promising tools for detecting local damage in steel bridges.

Determination of coupled solvent mass in quartz crystal microbalance measurements using deuterated solvents

A simple method is described for determining of the contribution of hydrodynamically coupled solvent to the adsorbed film mass determined in a quartz crystal microbalance (QCM) when operated in liquid. The method requires no additional apparatus and utilizes the change in QCM resonant frequency response between measurements made in nondeuterated and deuterated solvents. The mass of coupled water in a polymer film has been determined and is found to agree with that determined by XPS analysis of the dried polymer film.

An investigation of the spectral effect of multiple early reflections

The interaction of a direct sound with a single reflection of short delay is well-understood. Comb filtering is a quantifiable, measurable, inevitable result. In actual auditoria, one rarely hears a single early reflection. Typically a volley of several reflections follows the direct sound. This paper presents an analytical evaluation of the change in frequency response due to, not one, but several reflections. The combination of a direct sound with several early reflections does not result in a more pronounced, more audible comb filter quality. Rather, the interaction of the direct sound with each of the several reflections in combination with the interaction among the many reflections themselves tends to average out or randomize the expected, comb filtered, spectral distortion.

An Efficient, Accurate and Robust Radiometer Configuration for Microwave Temperature Measurement For Industrial and Medical Applications

The theoretical and practical design of a type of microwave radiometer particularly suited to industrial and medical temperature measurement is described. The use of sequential switching of source and reference signals with synchronous demodulation of switched signal components gives an efficient and robust instrument configuration. The radiometer measures the true, matched-impedance effective temperature of the coupled source. Changes in noise-figure, gain or frequency response of the radiometer microwave amplification do not affect the temperature measurement. Practical microwave radiometers using this configuration can be simply calibrated, and have inherently stable calibration and excellent accuracy.